Top officials who have been fired or quit under Trump administration

"General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems," Trump tweeted.

White House Chief of Staff John Kelly and Defense Secretary James Mattis are reportedly handling the search for McMaster's replacement. (Evan Vucci/AP)

The White House released a statement calling Thursday's report "fake news."

"I was just with President Trump and H.R. McMaster in the Oval Office. President Trump said that the NBC News story is 'fake news,' and told McMaster that he is doing a great job," White House spokesman Michael Anton said.